Hardfacing as a process generally refers to application of a hard and wear resistant material to the surface of a second material. When a hardfacing layer is applied to a second material that is a metal. The metal may be a pure metal or metal alloy. The hardfaced metal may be referred to as the base metal. The hard and wear resistant material may be a composite material which incorporates wear resistant particles in a matrix of a component, such as a metal.
Hardfacing application techniques frequently include welding and/or spraying. Welding may be defined as the joining of two or more pieces of metal by applying heat, pressure or both to produce a localized union through fusion or recrystallization across the interface (ASM Metals Reference Book, ed. M. Bauccio, 1993, ASM International). In fusion welding with a filler metal, both the filler metal and the base metal are melted together to complete the weld.
Fusion welding techniques include, but are not limited to, oxyfuel gas welding, resistance welding, laser beam welding, electron beam welding and arc welding. Gas metal arc welding (GMAW) is an arc welding process which produces coalescence of metals by heating them with an arc between a continuous filler metal (consumable) electrode and the workpiece. Shielding is obtained from an externally supplied gas or gas mixture. Variations of GMAW include short circuit transfer, globular transfer, spray arc transfer and pulsed arc transfer depending on welding parameters and equipment variation. GMAW may use an external shield gas that may be a largely inert gas, such as argon, a mixture of argon and other gases or a reactive gas such as carbon dioxide For GMAW welding direct current is typically used; the electrode may be either positive or negative.